Method and apparatus for treating metallic strands in hot dip coating



Jan. 23, 1962 E. L. KNAPP METHOD AND APPARATUS FOR TREATING METALLIC STRANDS IN HOT DIP COATING Filed Sept 26. 1960 JNVEN TOR. EAIZLE L/(NA PP t ATTORNEYS United States Patent Ofilice 3,018,190 Patented Jan. 23, 1962;

METHGD AND APPARATUS FOR TREATING METALLZQ STRANDS IN HOT DIP. COATING Earle L. Knapp, Kansas City, Mo., assignor to Armco Steel Corporation, Middletown, Ohio, a corporation of Ohio F iied Sept. 26, 1960, Ser. No. 58,270 6 Claims. (Cl. 11751) This invention relates to a process and an apparatus for treating metallic strands prior to hot dip coating and particularly where the coating metal is aluminum or an aluminum alloy.

In the Oganowski Patent No. 2,437,918 some of the problems in connection with obtaining good coatings of an aluminum or aluminum alloy on metallic strands by the hot dip method were discussed and in said Oganowski patent it was taught to provide a source of sodium vapor in a bell dipping into the coating metal so that'the sodium vapor would have access to the strand and would provide upon the surface of the bath through which'the strand entered a powdery layer comprising sodium aluminate. While said patent referred to sodium, it was explained that substantially like results could be obtained with other alkali metals as, for example, potassium and lithium.

The strand, prior to entering the aluminum bath according to the Oganowski patent, was given a pretreatment as described and claimed in the Sendzimir Patents Nos. 2,110,893 and 2,136,957, wherein the strand is first chemically cleaned and then dried and then passed through a high temperature reduction furnace and then a controlled cooling furnace before entering the molten coating metal.

In the said Oganowski patent, the strand entered downwardly into the bath and passed around a roll and emerged from the bath outside the hood.

In my earlier Patent No. 2,914,423 dated November 24, 1959, I disclosed and claimed an apparatus and a method for coating metallic strands in which the strand passed vertically upwardly through a hole in the bottom of a coating pot. The strand had been pretreated according to the Sendzimir patents and then passed through a so-called turn-up box and traveled vertically upward through the coating pot and on to a finishing operation.

With the foregoing considerations in mind, it is an object of the present invention to apply the teachings of the Oganowski patent to the coating of the strand as described in my said earlier Patent No. 2,914,423. While according to the present invention I utilize sodium vapor for the same ultimate purpose as Oganowski, I utilize it in a difierent way involving novel apparatus elements and novel method steps of which I shall now describe exemplary embodiments.

Reference is made to the drawing forming a part hereof and in which:

FIGURE 1 is a fragmentary cross-sectional view of a structure for supplying sodium vapor to the strand after the pretreatment portion of the apparatus and prior to its entry into the coating pot.

FIGURE 2 is an enlarged elevational view with parts broken away of a portion of the structure of FIGURE 1.

Briefly, in the practice of the invention I provide a holder for metallic sodium in communication with a tubular portion of the apparatus connecting the pretreatment apparatus with the coating pot. The holder is generally tubular and is disposed at an angle with its upper end communicating with the said tubular portion. The connection between the tubular portion of the apparatus and the holder, and the holder itself, may be insulated such that the heat of the strand melts the metallic sodium and causes it to be vaporized. Such reaction products as may be formed with the metallic sodium and 2v which may be principally sodium hydroxide, will. fall to the bottom of the holder so that the. molten sodium before vaporization etfectively floats on top of its. reaction products, whereby the molten elemental sodium is. closest to the hot strand from which it. can absorb heatfor vaporization.

Referring now in greater detail to the drawings, the end of the pretreatment apparatus. (this. may be the top of the turn-up box) is indicated at 19. A tubular. member 20 connects the exit from the member 19 with the bottom of the coating pot (not shown). The strand 15 passes vertically upward through the member 20. At 21 is shown a pipe through whichv a non-oxidizing or a reducing gas is fed, which gas flows oppositely to. the direction of movement of the strand and flows through a portion at least of the pretreatment apparatus.

According. to the present invention, the member 20 is provided with an opening 22 over which is secured, by welding or other suitable means, a tubular member 23. The precise angle at which the member 23 isdisposed is not critical but it should be upwardly directed with respect to the. opening 22. Suitablysecured to the lower end of the member 23 is a collar or the like 24 provided with bolt holes 25 and having the annular shoulder 26.

The member 23 is closed at its. lower end by means of a member 27 which may be similar in configuration to the member 24 and is provided with the mating bolt holes 28. The member 27 is either solid or plugged as. at 29 and has an annular groove '30 into which. the annular shoulder 26 is adapted to enter. A suitable gasket 31 is seated between the shoulder 26 and the groove 30 to provide a gas-tight seal.

The member 27 is secured in place by means of bolts 32.

The member 23 and its associated parts thus constitute a holder within which is placed a cartridge indicated generally at 33 in FIGURE 1 and shown in detail in FIG- URE 2. This cartridge is simply a piece of thin walled steel tubing plugged at its lower end as at 35 and open at its upper end and provided with a wire loop 34 for handling.

The metallic sodium is placed in the cartridge 33 and the cartridge is then slipped into place in the holder 23 and held in place by the member 27. In FIGURE 1 the molten sodium has been indicated diagrammatically at 36 and the molten reaction products at 37, and it will be seen that the molten elemental sodium floats on top of its reaction products Where it is subjected to the heat of the strand 15. The use of the metal cartridge contributes greatly to safety in handling of the metallic sodium. When the metallic sodium is depleted, it is a simple matter to remove the cartridge 33 and replace it with a fresh cartridge charged with fresh metallic sodium. The heat of the strand melts the metallic sodium and brings about its vaporization. The rate of vaporization of the molten sodium is a function of the amount of radiant heat absorption and of the amount of insulation around the holder 23 and the tubular element 20. Such insulation is shown at 38. With very small cross-sectional area strands, the holder 23 and the adjacent portion of the member 20 must be well insulated. The larger the cross-sectional area of the strand being treated, the less insulation is required. I have found that if the strand is wire and if its diameter is A1, inch, no insulation is required. The proper amount of insulation for the particular size strand being coated can readily be determined by one skilled in the art.

While I do not wish to be bound by theory, it is my opinion that the basic function of the sodium vapor in this process is to modify the oxide film which may be on the surface of the bath of coating metal through which the strand ultimately passes, and that the sodium may cleanse the molten aluminum which contacts the sodium treated strand, of dissolved gases and entrapped microscopic oxide particles, as well as scavenging the atmosphere of minor percentages of oxygen which may have infiltrated this portion of the apparatus.

Regardless of any theory as to what the sodium accomplishes, it appears to improve the wetting characteristics of the molten aluminum on the clean strand so that the aluminum appears to be more fluid and the resultant coating is much more brilliant.

When I speak of molten aluminum in the claims, it will be understood that this language is inclusive of alloys of aluminum with small percentages of such metals as silicon, beryllium, magnesium and the like.

Having now fully described my invention, what I claim as new and desire to secure by Letters Patent is:

1. In an apparatus for coating a metallic strand with molten aluminum, wherein the strand, after undergoing a pretreatment, is caused to move vertically upward and through a hole in the bottom of a coating pot containing molten aluminum, and wherein said strand, in passing from the pretreatment portion of the apparatus to the coating pot, passes through a tubular member into which a non-oxidizing gas is fed; a branch fitting disposed at an angle'less than a right angle with respect to said tubular member and communicating therewith in an upward direction, said branch fitting having means for closingit at its lower end, and means for holding a supply of metallic sodium in said branch fitting.

2. A structure according to claim 1, wherein said last named means comprises a tubular open top cartridge removably disposed in said branch fitting.

3. A structure according to claim 2, wherein said cartridge is of thin walled steel tubing and is provided with hand grip means.

4. A structure according to claim 1, wherein the closing means for said branch fitting has sealing means providing a gas-tight seal with said fitting.

5. A structure according to claim 1, wherein said tubular member, at the region of said branch fitting, and said branch fitting, are covered with heat insulating material.

6. In a process of coating a metal strand with molten aluminum, wherein the strand, after undergoing a pretreatment, is caused to move vertically upward and through a hole in the bottom of a coating pot containing molten aluminum, and wherein said strand, in passing from the pretreatment portion of. the apparatus to the coating pot, passes through a tubular member into which a non-oxidizing gas is fed; the steps of enhancing the wettability of said strand by said aluminum and thus improving the quality and appearance of the aluminum coated strand, which include causing said strand while hot and before it enters said coating pot, to melt and vaporize metallic sodium, causing said vaporized sodium to contact the strand in admixture with said non-oxidizing gas, and protecting said strand from the atmosphere up to its entry into the coating metal.

References Cited in the tile of this patent UNITED STATES PATENTS Knapp Nov. 24, 1959 

6. IN A PROCESS OF COATING A METAL STRAND WITH MOLTEN ALUMINUM, WHEREIN THE STRAND, AFTER UNDERGOING A PRETREATMENT, IS CAUSED TO MOVE VERTICALLY UPWARD AND THROUGH A HOLE IN THE BOTTOM OF A COATING POT CONTAINING MOLTEN ALUMINUM, AND WHEREIN SAID STRAND, IN PASSING FROM THE PRETREATMENT PORTION OF THE APPARATUS TO THE COATING POT, PASSES THROUGH A TUBULAR MEMBER INTO WHICH A NON-OXIDIZING GAS IS FED; THE STEPS OF ENHANCING THE WETTABILITY OF SAID STRAND BY SAID ALUMINUM AND THUS IMPROVING THE QUALITY AND APPEARANCE OF THE ALUMINUM COATED STRAND, WHICH INCLUDE CAUSING SAID STRAND WHILE HOT AND BEFORE IT ENTERS SAID COATING POT, TO MELT AND VAPORIZE METALLIC SODIUM, CAUSING SAID VAPORIZED SODIUM TO CONTACT THE STRAND IN ADMIXTURE WITH SAID NON-OXIDIZING GAS, AND PROTECTING SAID STRAND FROM THE ATMOSPHERE UP TO ITS ENTRY INTO THE COATING METAL. 